Transcriptomic Signatures in Seeds of Apple (Malus domestica L. Borkh) during Fruitlet Abscission

Abscission is the regulated process of detachment of an organ from a plant. In apple the abscission of fruits occurs during their early development to control the fruit load depending on the nutritional state of the plant. In order to control production and obtain fruits with optimal market qualities, the horticultural procedure of thinning is performed to further reduce the number of fruitlets. In this study we have conducted a transcriptomic profiling of seeds from two different types of fruitlets, according to size and position in the fruit cluster. Transcriptomic profiles of central and lateral fruit seeds were obtained by RNAseq. Comparative analysis was performed by the functional categorization of differentially expressed genes by means of Gene Ontology (GO) annotation of the apple genome. Our results revealed the overexpression of genes involved in responses to stress, hormone biosynthesis and also the response and/or transport of auxin and ethylene. A smaller set of genes, mainly related to ion transport and homeostasis, were found to be down-regulated. The transcriptome characterization described in this manuscript contributes to unravelling the molecular mechanisms and pathways involved in the physiological abscission of apple fruits and suggests a role for seeds in this process.

脱落（Abscission）是植物器官发生受控脱离的调控过程。在苹果中，果实脱落发生于果实发育早期，用于依据植株营养状况调控坐果量。为调控产量并获得具备最优市场品质的果实，园艺生产中会通过疏果操作进一步减少幼果数量。本研究针对果簇中按大小与着生位置划分的两类幼果的种子，开展了转录组表达谱分析（transcriptomic profiling）。通过RNA测序（RNA-seq）获取了果簇中央与侧生幼果种子的转录组表达谱。借助苹果基因组的基因本体（Gene Ontology, GO）注释，对差异表达基因进行功能分类以开展比较分析。研究结果显示，参与胁迫响应、激素生物合成以及生长素与乙烯的响应/转运过程的基因呈现过表达状态；另有少量主要与离子转运及稳态维持相关的基因表现为表达下调。本研究描述的转录组特征解析，有助于阐明苹果果实生理性脱落相关的分子机制与通路，并提示种子在该过程中发挥的作用。